Internal permanent magnet motors can have the highest power density of any electrical motor available today. They are used in vehicular, industrial, and commercial applications, in both the inner- and outer-rotor configurations. The outer-rotor configuration is used in vehicular applications for its reduced size and increased torque density. The same trend has dictated the design of surface-mounted permanent magnet motors for vehicular applications, but these motors do not have the extended speed range that is desired in products which are intended to provide high performance. Some compromises have been made to develop the current generation of internal permanent magnet motors which do possess this extended speed range, including a reduction in maximum torque.
Starting torque is generally proportional to a motor's size, winding fill factor, and material composition. Small size is important in vehicle applications, so large motors with high torque are still undesirable. High fill-factor motors may achieve higher torque and higher efficiency, but there is in equivalent increase in cost and manufacturing complexity. Expensive, high-performance materials are likewise prohibitive in terms of cost. The remaining frontier in motor development is material utilization and motor design.